Tapered magnetic core



p T w. E. NEWMAN 2,427,872

TAPERED MAGNETIC CORE Fi led March 24, 1943 VVilliam E. Newman (IttomegPatented Sept. 23, 1947 2,427,872 'raranan MAGNETIC cons William E.Newman, Mooreatown, N. J., assignor to Radio Corporation of America,a/corpora tion of Delaware Application March 24, 1943, Serial No.480,342

Claims. (0141541) This invention relates to variable permeability tuningapparatus for use in radio and analogous systems for the communicationof intelligence.

In variable inductance devices of the type-- wherein inductancevariations are effected by the movements of a magnetic core, withrespect to an inductance coil, it is common practice to employ a core oftapered construction in order to achieve a desired relation between thetotal tuning movement or "stroke" and the inductance, variation. Where,as is usually the case, the coil is mounted upon a hollow formof'uniform diameter and the core is mounted for movement in or throughthe interior of the coil-form, a conventionally tapered core may tilt orwobble within the bore of the form. Such undesired displacement of thecore within the coil-form may cause the tuning mechanism to jam or togive rise to other less apparent mechanical and electrical difllculties.

Accordingly, the principal object of the present invention is to providean improved variable permeability tuner of the type employing a taperedcore, and one which obviates the foregoing and other objections topresent day permeability tuners.

Another and related object of the present invention is to provide animproved tapered" magnetic core of novel construction and one capable ofuse with a standard coil and form of conventicnal shape and dimensions.

Another and important object of the present invention is to provide animproved "tapered magnetic core, and one which lends itself readily tothe adjustment of its eifective permeability,

and this, too, without change in its overall dimensions.

The foregoing and related objects are achieved in accordance with theinvention in a cylindraceous magnetic core of uniform overall dimensionsby providing the core with one or more axially extending grooves orflutes of gradually varied depth and/or width and which may be separatedone from another either by common arris or by a narrow fillet upon whichthe core slides within the coil-form. The permeability of cores made inaccordance with the present invention may be adjusted, at least over alimited range, by applying a quantity of comminuted magnetic material(e. 3.. iron or the ore magnetite) in a plastic carrier -(e.- g.,Polystyrene) into one or more of the grooves or flutes.

Certain preferred details of construction will be apparent and theinvention itself will be best understood by reference to the accompanyidrawing, wherein:

Figure 1 is a plan view looking into the leading end of a magnetic coreconstructed in accordance with the principle, of the invention.

Figure 2 is a longitudinal sectional view taken on the line 11-11 ofFigure 1, and

Figure 3 is a projected side elevational view of the core of Figures 1and 2.

Figure 4 is a plan view looking into the leading end of another magneticcore within the invention.

Figure 5 is a longitudinal'sectional view taken on the line V--V ofFigure 4, and

. Figure 6 is a projected side elevational view of the magnetic core ofFigures 4 and 5.

Figure 7 is a plan view looking into the leading end of a modificationof magnetic core within the invention, and

Figure 8 is a projected side elevational view of the core of Figure 7.

Figure 9 is a plan view, partly in section, of a neticvcore within theinvention.

In the drawings, wherein like reference characters designate the same orcorresponding parts in all figures, M (Ml, M2, etc.) designatesgenerally a magnetic core, which is cylindrical in outline, andconstituted of mutually insulated comminuted particles or granules ofthe ore magnetite or of powdered iron, molded in a known manner. Thediameter of the core M is such as to give it a sliding fit within thebore of its coil-form F (see Figure 9) when a suitable force is appliedthereto as through a threaded brass rod R (Figures 2, 3, 5, 6 and 8) orthrough a pair of oppositely located eyelets E (Figure 9) which areembedded in the core prior to the molding operation.

Substantially any desired relation between the total tuning movement or"stroke of the core and the resulting change of inductance of the coilwith which it is associated is achieved, in accordance with theinvention, by providing the core with one or more longitudinal flutes orgrooves of gradually varied depth and/or width. Thus,

with four longitudinally extending circumferentially spaced grooves G,which are separated one from another by narrow fillets T which serve toprevent the core from tilting while it is within its coil form. In thisembodiment of the invention the grooves G have substantially flat bottomsurfaces and are tapered both as to width and depth from the leading endof. the core, where the grooves are of maximum width and depth,

variable permeability tuner incorporating a mag-,

in the embodiment of the invention shown in Figures 1, 2 and 3 themagnetic core M is provided 3 to points adjacent to the opposite ortrailing end of the core. These grooves are preferably formed in acomplementarily shaped mold (not shown) in which case the mold may beparted along a. line (a--a, Figure 1) whichcoincides with the maximumdiameter of the core.

In the embodiment of the invention shown in Figures 4, 5 and 6, themagnetic core, which'is here designated. MI, is provided with but-ftwoflutes GI which are separated one from another by relatively widefillets Tl.

1-3, are curved laterally and longitudinally to provide a desiredvariable inductance-characteristic for the coil assembly for which-thecore is designed. As in the earlier described embodimerit of theinvention the maximumdepth of the flutes or grooves G! is adjacent'tothe-leading end of the core.

The magnetic core"M2 shown in Figures 7 and 8 is provided with threedepressions or grooves G2 which terminate in three equally spacedrounded edges T2 at the leading end of the core, as shown in Figure 7.Since, as above indicated, the contour anddimensions of the grooves, aswell as their number, will ordinarily be chosen with regard to theparticular inductance-changing characteristic desired, it will beapparent that these grooves G2 may be either flat or curved and may beof uniform (instead of tapered) width, if desired. I

Figure 9 shows a-variable permeability tuner incorporating a taperedmagnetic core M3 constructed in accordance with the principle of theinvention. This core is mounted for movement within and with respect toa tuning coil A which is wound upon an open-ended coil form F of uniformdiameter. The core M3 is driven by a cord B which extends around a pairof pulleys C and carries an index or pointer D which cooperates with asuitably calibrated elongated dial scale E. The core M3 and, hence, thepointer D are moved by means of a tuning knob, not shown, but which maybe mounted on the end of a tuning shaft S.

The length of the magnetic core M3 and of the inductance coil A and dialscale E may be the same as disclosed in co-pending application, SerialNo. 460,303, to Wendell L. Carlson, flied September 30, 1942, now PatentNo. 2,370,714,

grantedMarch 6, 1945. That is to say, when an elongated dial scale isemployed the length of the magnetic core M3 is preferably made at leasttwice that of the coil A to avoid the use of a gear train, or the likefor correlating the stroke of the variable inductor with that of thetuning index or pointer D.

It is well known that small variations in the amount or quality of thecore materials may result in variations in the magnetic properties ofthe cores. To compensate for such variations it has heretofore beenproposed to attach a suitable quantity of magnetic material in the formof a pellet to the leading end of the core, Since a cavity or otherauxiliary means must be pro- These flutes G 'p'lastic carrier, such aspolystyrene, into one or unlike the flat grooves G of thecore.of,Fi8ures.

vided for holding the pellet in position, this prior art method ofadjusting the effective permeability of a magnetic core is not alwayspractical, especially in the case of a core provided at its ends with. ascrew or with eyelets or other adjusting means. As shown in Figure 9 thepermeability of a grooved core within the present inyentio'n may beadjusted by applying a small quantity oi. comminuted magnetic material,such as powdered iron or magnetite, in an adhesive or mgr? ofthe flutesor grooves G3 as indicated at From the foregoing it is apparent that the-present invention provides an improved tapered magnetic corecharacterized by its novel construction, its ease of adjustment, and byits trouble-free performance. What is claimed is:

1. A magnetic core adapted for insertion into a coil-form which has acylindrical bore therein, said core comprising a cylindraceous elementhaving a maximum diameter throughout the greater portion of its lengthcorresponding substantially to the diameter of said bore and providedwith a longitudinally extending depression of tapered depth on thesurface thereof which is presented to the inner surface of the bore ofsaid coil form.

2. The invention as set forth in claim 1 and wherein the maximum depthof said longitudinal depression is adjacent to the end of said elementwhich is first presented to said coil form.

3. The invention as set forth in claim 1 and wherein said longitudinaldepression is of tapered 'width, and the maximum width of saiddepression is adjacent to the end of said element which is firstpresented to said coil form.

4. A device of the character described comprising a tapered coreconstituted of mutually insulated magnetic particles and provided on itstapered surface with a plurality of longitudinally extending raisedportions for guiding said core within the bore of a coil form.

5. A magnetic core adapted for insertion into -a coil form which has acylindrical bore therein, said 'core comprising a cylindraceous elementhaving a maximum diameter throughout the greater portion of its lengthcorresponding substantially to the diameter of said bore, whereby saidcore has a sliding fit within said core, and

provided on its outer surface with a longitudinally The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,141,890 Weis Dec. 27, 19382,245,373 Weis et a1. June 10, 1941

